Two-stage flow target for well control apparatus



Aug. 22, 1967 A. D. BOGGS TWO-STAGE FLOW TARGET FOR WELL CONTROL APPARATUS Filed 001:. 6, 1964 M w m I 0 \\'Z\ 2? 5 H [II I H] INVENTOR ALI/AH 0 E0668 BY F6 United States Patent Ofiice 3,336,947 Patented Aug. 22, 1967 3,336,947 TWO-STAGE FLOW TARGET FUR WELL CONTROL APPARATUS Alvah D. Boggs, New Orleans, La., assignor to Chevron Research Company, a corporation of Delaware Filed Get. 6, 1%4, Ser. No. 401,869 2 Claims. (Cl. 137-800) This invention relates to methods and apparatus for controlling fluid flow from oil and gas wells and, more particularly, this invention relates to an improved two-stage flow target for receiving high velocity fluid flow from a production choke in oil well control apparatus.

In the petroleum producing art it is often necessary or desirable to limit the production of the petroleum fluids from a well to a value less than would result if the well were allowed to flow wide open through the well tubing. A particular example of this is the case where a single well is producing through concentric production strings from more than one zone and it is desired to maintain production from the zones at a certain ratio. Therefore one or more of the zones must be produced at something less than full capacity. The most common method of controlling production is to install apparatus in the well tubing to restrict the flow through the tubing. These apparatus are commonly known as production chokes or more simply, chokes.

Production chokes are sized to limit flow through the tubing to a desired value. However, since the producing zones are often at very high pressure, the flow from the downstream end of the choke is usually at extremely high velocity. In many instances the high velocity\flow causes abrasion and cutting of the surfaces it contacts. This is a serious problem where sand or other abrasive particles are present in the production fluids. The problem is especially troublesome in Wellhead control apparatus which must often be located in a confined space thus making compact apparatus necessary, Generally wellhead control apparatus, including wellhead manifolds and other choke boxes, have metal surfaces which are exposed to high velocity flow at the downstream end of a choke and these surfaces suffer from abrasion by the fluid.

The problem has been recognized in the art and attempts have been made to solve it. Devices known as flow targets have been placed in the path of the high velocity fluid stream to take the force of it. The earliest flow targets heretofore used presented a relatively abrasion-resistant surface to the high velocity stream. The abrasion-resistant surface deflected the stream and reduced its energy. Flow targets of this type are shown in US. Patents Nos. 2,590,-

688 and 2,943,640. Generally the flow target of the prior art comprised a body member having an insert for deflecting the fluid stream passing through the choke. The insert was made of abrasion-resistant material such as lead, tungsten carbide or a ceramic. However, in field operation the flow targets heretofore known have not proved suitable because of the rapid abrasion and wear of the insert. This is especially true in producing from fields which flow a lot of sand in the produced petroleum fluids.

A further development made recently in the art is the use of a plug having a blind bore alignable with the flow axis of the choke. This advance is described and claimed in copending application Ser, No. 216,556, now US Patent No. 3,156,261, of Garland Cason which application is assigned to the assignee of the present invention. As described in that application a plug having a blind bore of a predeterminable depth in relation to its diameter is connected to the well manifold and aligned with the fluid stream. It has been found that this is an effective means of absorbing the energy of the fluid stream. It has also been found however that in Wells producing a large excess of sand and, particularly in wells where a large excess of sand is produced through a choke that is wholly or partially defective in alignment, that the wall of the plug described in the above-mentioned application has a tendency to be cut through.

Briefly the present invention provides an improved twostage fluid cushion flow target for mounting on a well manifold on a conduit downstream of and in line with a production choke comprising means forming a blind borehole, said blind borehole being alignable with the flow axis of a production choke and having a first stage of substantially circular cross section with a diameter. no greater than the diameter of the conduit downstream of the production choke and a second stage of substantially circular cross section with a diameter of at least twice the diameter of said first stage, said first stage having a length to diameter ratio of not more than three to one and said second stage having a length greater than its diameter and means for mounting said means forming said blind borehole on wellhead control apparatus.

Means are provided to mount the blind bore on a choke box or the like in the flow path of a production choke to receive the high velocity fluid stream from the choke. The two stages or portions of the blind borehole cooperate to retain a portion of the fluid from the fluid stream to serve as a cushion for the later impringing stream. The energy of the high velocity stream is absorbed by the fluid cushion and abrasion of the surfaces of the flow target is thus prevented.

It is a particular object of this invention to provide an improved two-stage flow target for a production choke in wellhead control apparatus, which two-stage flow target makes use of fluid to direct and to cushion the impinging fluid stream from the choke and which flow target is especially useful in wells producing large quantities of sand.

Other objects and advantages of the present invention will be apparent from the following detailed description read in light of the accompanying drawing which is a part of this specification and in which:

FIGURE 1 is a sectional view of one type of wellhead control apparatus showing the preferred embodiment of the improved two-stage flow target of the present invention.

FIGURE 2 is a longitudinal sectional view of the preferred embodiment of the apparatus of the present invention.

FIGURE 3 is section 3-3 of FIGURE 2.

FIGURE 4 is section 4-4 of FIGURE 2.

With particular reference to FIGURE 1, one type of apparatus for controlling the flow of petroleum fluids from a producing well is shown. The wellhead control apparatus shown in FIGURE 1 is a wellhead manifold 60. The manifold 60 is a dual manifold useful in controlling flow from a well having more than one producing zone. It is described in detail in US. Patent 2,943,640. However, a brief description of the manifold and its operation is given below and it is useful in understanding the improvements provided by the present invention. Generally when a production choke is used in wellhead control apparatus, a flow target is also used to receive the high velocity flow from the choke and to absorb the energy of the fluid stream. This is particularly true of wellhead control apparatus such as illustrated in FIGURE 1 where close tolerances in the apparatus require conduits with sharp corners immediately after the choke.

In the manifold of FIGURE 1 the flow of petroleum fluids enters manifold 60 from the well via appropriate tubing to passage 22. The petroleum fluids then enter duct 26 by way of passage 24. Valve stem 30 and valve seat 32 control flow in duct 26 between passage 24 and conduit 20. A choke 40 having a restricted flow path 41 is positioned in conduit 2% to control the flow of fluid through conduit 29. A high velocity fluid stream results in conduit 20 downstream of choke 40 as the well fluids pass through the restricted opening 41 of the choke 40 and enter the downtsream portion of conduit 29. The petroleum fluids then enter the blind bore of the improved two-stage flow target of the present invention, which target is represented generally by the numeral 44. The flow target 44 expends the energy of the high velocity fluid stream. The fluid leaves the welhead control apparatus by means of duct 46 and conduit 48. Valve stem 50 and valve seat 52 control flow of fluids leaving duct 46.

It has been found that wellhead control apparatus is particularly vulnerable where a conduit makes a sharp turn immediately downstream of a choke. This is particularly true in wells producing a large amount of sand. Heretofore flow targets have been used to deflect the fluid stream passing from the choke. These targets are expensive and are subject to rapid wear. This is also true of the straight blind bore target of the above-cited application particularly when severe sand conditions exist and when the choke is damaged causing turbulence in the fluid stream entering the blind bore flow target which diverts the stream against the wall of the target. It has been found that under these conditions the wall of the plug forming blind bore will be cut out.

The present invention provides an improved two-stage flow target, generally represented as 44 in FIGURE 1, which provides a fluid cushion for the impinging fluid stream passing from the choke and also directs the fluid stream away from the wall of the plug forming the blind bore. The present target is particularly useful in wells where a high percentage of sand is produced and where damage to the choke causing diverted flow is likely.

Referring now to FIGURE 2, FIGURE 3, and FIG- URE 4, a preferred form of apparatus assembled according to the present invention will be more completely described. The present invention provides a two-stage flow target 44 for wellhead control apparatus comprising means forming a blind borehole and means for aligning the blind borehole to receive high velocity fluid flow from a choke. In the preferred embodiment the means forming the blind boreholde includes a plug 62. A first stage 61 of a blind borehole extends interiorly of plug 62 a substantial distance from the upstream end 63 of plug 62. The first stage 61 of the blind borehole has a generally circular cross section and has a diameter no greater than the diameter of the conduit 20 immediately downstream of the choke 40 with which it is to be aligned. The length of the first stage 61 of the blind bore is no greater than three times the diameter of the first stage 61.

A second stage 71 is also provided in the blind bore. The second stage 71 is formed downstream from the first stage 61 and also has a generally circular cross section. The diameter of the second stage 71 is at least twice the diameter of the first stage 61. For best results the diameter of the second stage is no more than three times the diameter of the first stage. The length of the second stage 71 of the blind bore is at least 1 /2 times greater than its diameter and it is preferably about two times its diameter. The short transitional stage between the stages 61 and 71 is kept as small as possible. For purposes of measurement the first stage ends at the beginning of the transition as indicated by the phantom line in FIGURE 2. The transition is included when measuring the length of the second stage.

A preferred means for aligning the plug 62 forming the blind borehole in position on a wellhead control apparatus to receive the high velocity flow from a choke is provided by flange 65. The flange is provided with suitable holes 66 for mounting on well control apparatus such as the well manifold of FIGURE 1. The longtudinal center line of both the first stage 61 and the second stage 71 of the blind borehole is alignable with the flow axis of the choke. Thus both stages of the blind borehole have a common longitudinal axis.

When the plug 62. is mounted on the wellhead apparatus the longitudinal axis of the blind borehole is aligned with the flow axis of the choke. If the blind borehole is not aligned with the flow axis of the choke the fluid stream passing through the choke will not be cushioned in the blind borehole and damage to the flow target will occur. Packing rings 68 provide for a fluid-tight seal when the flow target 44 is mounted.

The blind borehole including both the first and second stages extends a substantial distance interiorly of plug 62 from the upstream end 6-3. The longitudinal axis of the blind borehole is preferably identical to the longitudinal axis ofplug 62 which forms it. The first and second stages of the blind hole have circular cross sections and both stages are symmetrical about the longitudinal axis. According to the present invention the total blind borehole must be of sufficient depth to provide a fluid cushion for the impinging fluid stream. In this manner abrasion which causes damage and wearing out of the metal surfaces of conventional flow targets is prevented. The first and second stages of the blind bore cooperate to provide a sump for the temporary collection of a portion of the high velocity fluid entering it. The continually col lected fluid then serves to cushion the later arriving high velocityfluid as it enters the blind borehole. The fluid in the blind borehole absorbs the energy of the fluid stream and the flow target of the present invention is not subject to wear from abrasion.

The apparatus of the present invention is particularly resistant to side wall wear. That is the first and second stages of the blind bore cooperate in a manner to prevent abrasion by the sand in the impinging fluid stream not only to the rear portion of the flow target but also to the side walls of both the first and second stages. This is particularly noticeable when a defective choke is present in a choke box. Prior art flow targets having only a straight bore were subject to severe side wall wear, which in a relatively short time, would cut through the target. The present invention overcomes this problem. While the reason for this is not entirely understood it is believed that the first and second stages cooperate in a manner to redirect the fluid stream away from the wall of the plug to not only prevent cutting out of the back of the target but to also reduce, if not eliminate, side wall wear to both the walls of the first and second stages.

It is an important aspect of the present invention that inserts of the type heretofore used in flow targets are un necessary and are dispensed with by the improved flow target. However, it is within the scope of the present invention to provide an insert in the flow target body provided that the insert does not interfere with the dimensions of the blind borehole according to this specification. Generally, however, it is preferred to machine the flow tar-get of the present invention from a single piece of stock and thus dispense with inserts of any type. In this respect although the hole formed in accordance with the invention has been termed a blind bore it is obviously not intended to limit the invention to only bored holes. Obviously any type of forming is within the scope of the invention. And also the means forming the blind hole may be made up of one or of many pieces of stock.

A demonstration to show the improved results of the two-stage fluid cushion flow targets of the present invention compared to conventional fluid cushion flow targets having a straight bore, occurred in wells in the Gulf Coast area. The wells were producing through a production choke. The chokes were part of a wellhead manifold. The particular manifolds in use on these wells were similar to that shown in FIGURE 1. An improved twostage flow target assembled according to the present in vention was installed in the positive choke section of the manifold. The diameter of the first stage of the blind borehole of the improved flow target was about 1 inch.

1 tested in wells of the The length of the first stage of blind borehole was about 2 /2 inches. The diameter of the second stage of the blind borehole was about 2 inches and the length of the second stage was about 4 inches.

This improved two-stage fluid cushion flow target was Venice District in Main Pass Block 69 Field, Plaquemines Parish, La. The two-stage target was used on Louisiana Stage 1277 #10 1) well which produces an excessive amount of sand. The two-stage target was operated for nine days and showed no sign of damage. The two-stage target was removed because a Workover operation was to be performed on the well. In contrast to the above a straight blind bore target was placed on the same well and its wall was cut out in 28 hours. A second straight bore target having a ceramic liner was then installed on this well and again was cut out in approximately 28 hours.

The above improved two-stage fluid cushion flow target was later placed on another heavy sand producing well, Louisiana State 1277 #G-4. Straight bore fluid cushion targets of the prior art had been lasting a week to ten days on this well before cutting out. The straight bore targets usually failed in the side wall. In contrast the improved two-stage fluid cushion target remained on the well for 21 days and was then removed. Visual inspection of the target revealed the only wear to be a small crater in the bottom center of the base approximately A in depth.

The two-stage target of the present invention alleviates the tendency to wear on the wall of the target and thus gives a greater life expectancy especially in heavy sand producing wells where damage or wear of the choke may cause a turbulence in the fluid stream emerging from the downstream end of the choke. It is believed that the critical dimensions of the two-stage target causes a counterturbulence that directs the main stream of the fluid from the choke back to the center of the target. Thus cutting out of the side walls of the target is prevented while still retaining the fluid cushion effect in the second stage of the target.

As has been fully described and illustrated, the present invention provides an improved two-stage target for use with wellhead control apparatus. The invention is not to be limited to the specific examples set forth in this specification but only by the scope of the appended claims.

I claim:

1. Animproved two-stage fluid cushion flow target for use in combination with wellhead control apparatus for receiving high velocity fluid from a choke positioned in a conduit of wellhead the control apparatus comprising plug means forming a blind borehole having a first stage of substantially circular cross section with a diameter of no greater than the diameter of the conduit immediately downstream of the choke from which it is to receive flow and a second stage of substantially circular cross section with a diameter of at least twice the diameter of the first stage, the first stage and the second stage having a common longitudinal center line, said first stage having a length to diameter ratio of not more than 3 to 1, said second stage having a length of at least 1 /2 times its diameter, and means for mounting said plug means on Wellhead control apparatus so that the blind borehole is aligned with the flow axis of a production choke.

2. The How target of claim 1 further characterized in that the length of the second stage is at least twice its diameter and the diameter of the second stage is between 2 and 3 times the diameter of the first stage.

References Cited UNITED STATES PATENTS 160,206 2/1875 Knowles 138-26 2,943,640 7/1960 James 137-594 3,156,261 11/1964 Cason 166--91 WILLIAM F. ODEA, Primary Examiner.

H. COHN, Assistant Examiner. 

1. AN IMPROVED TWO-STAGE FLUID CUSHION FLOW TARGET FOR USE IN COMBINATION WITH WELLHEAD CONTROL APPARATUS FOR RECEIVING HIGH VELOCITY FLUID FROM A CHOKE POSITIONED IN A CONDUIT OF WELLHEAD THE CONTROL APPARATUS COMPRISING PLUG MEANS FORMING A BLIND BOREHOLE HAVING A FIRST STAGE OF SUBSTANTIALLY CIRCULAR CROSS SECTION WITH A DIAMETER OF NO GREATHER THAN THE DIAMETER OF THE CONDUIT IMMEDIATELY DOWNSTREAM OF THE CHOKE FROM WHICH IT IS TO RECEIVE FLOW AND A SECOND STAGE OF SUBSTANTIALLY CIRCULAR CROSS SECTION WITH A DIAMETER OF AT LEAST TWICE THE DIAMETER OF THE FIRST STAGE, THE FIRST STAGE AND THE SECOND STAGE HAVING A COMMON LONGITUDINAL CENTER LINE, SAID FIRST STAGE HAVING A LENGTH TO DIAMETER RATIO OF NOT MORE THAN 3 TO 1, SAID SECOND STAGE HAVING A LENGTH OF AT LEAST 1/12 TIMES ITS DIAMETER, AND MEANS FOR MOUNTING SAID PLUG MEANS ON WELLHEAD CONTROL APPARTAUS SO THAT THE BLIND BOREHOLE IS ALIGNED WITH THE FLOW AXIS OF A PRODUCTION CHOKE. 